In the law, a proximate cause is an event sufficiently related to a legally recognizable injury to be held to be the cause of that injury. There are two types of causation in the law: cause-in-fact, and proximate (or legal) cause. Cause-in-fact is determined by the "but for" test: But for the action, the result would not have happened.

A proximate cause is an event which is closest to, or immediately responsible for causing, some observed result. This exists in contrast to a higher-level ultimate cause (or distal cause) which is usually thought of as the "real" reason something occurred.

Example: Why did the ship sink?

Proximate cause: Because it was holed beneath the waterline, water entered the hull and the ship became denser than the water which supported it, so it could not stay afloat.

Ultimate cause: Because the ship hit a rock which tore open the hole in the ship's hull.

In most situations, an ultimate cause may itself be a proximate cause for a further ultimate cause. Hence we can continue the above example as follows:

Example: Why did the ship hit the rock?

Proximate cause: Because the ship failed to change course to avoid it.

Ultimate cause: Because the ship was under autopilot and the autopilot's data was inaccurate.

(even stronger): Because the shipwrights made mistakes in the ship's construction.

(stronger yet): Because the scheduling of labor at the shipyard allows for very little rest.

(in absurdum): Because the shipyard's owners have very small profit margins in an ever-shrinking market.

Separating proximate from ultimate causation frequently leads to better understandings of the events and systems concerned.